The act of inserting an erect penis into a menstruating girl's vagina to check for blood similarly as one would check for oil in an automobile. It is also a good way to measure the depth of a woman's vagina. If a large enough man measures his own length prior to dipsticking, the amount of "oil" on his penis post-dipsticking will determine her depth.

Remember that during dipsticking it is important to wipe the dipstick off before you check for oil to yield sufficient results. It's got to be clean, and you have to give it a good swab."